1. Field of the Invention
The present invention relates generally to a coupling structure of a variable length shaft used for a steering device etc of an automobile, and more particularly to a coupling structure of a variable length shaft capable of enhancing a workability when assembling the steering device into a vehicle and surely preventing a "backlash" from being caused after having incorporated the steering device.
2. Related Background Art
A steering device of an automobile is structured such that an intermediate shaft of a steering shaft is contractible upon a collision etc of the vehicle, thus protecting the driver. More specifically, the intermediate shaft of the steering shaft is spline- or serration-fitted to a pipe member provided posterior to the intermediate shaft, and when the collision happens, the intermediate shaft is retracted into the pipe member.
On such spline-fitting or the like, a "backlash" might occur to some extent between the intermediate shaft and the pipe member due to factors such as a limit of working accuracy etc.
Japanese Utility Model Post-Exam Publication No. 63-17862 discloses a structure for preventing the "backlash" described above, wherein an end of a pipe member is capable of expanding and diminishing in diameter in a radial direction by forming a plurality of slits in the end of the pipe member, an intermediate shaft is spline-fitted in this pipe member, thereafter a ring member is fitted to an outer periphery of the end of the pipe member, and the end of the pipe member is fastened against the intermediate shaft, thereby preventing the above "backlash".
Before assembling the steering device into the vehicle, however, as disclosed in the above Publication, if the "backlash" is prevented by previously fastening the end of the pipe member with the ring member, a slide frictional resistance in an axial direction between the intermediate shaft and the pipe member increases on the contrary, in assembling the steering device into the vehicle. This might lead to a difficulty of adjusting lengths of the intermediate shaft and the pipe member in the axial direction and to a decline of workability.
Under such circumstances, it is desired that the workability be enhanced, when assembling the steering device into the vehicle, by enabling the intermediate shaft to move in the axial direction along inside the pipe member, and the occurrence of the "backlash" be prevented with certainty after having assembled the steering device.